This project focuses on the postnatal development of central brain stem pathways associated with sensory input from the upper respiratory tract and with sleep and autonomic physiology. The project is designed to determine the synaptic development within the nucleus tractus solitarius, which is the primary sensory nucleus of the IX and the X nerves; the locus coeruleus which synaptically interacts with the nucleus tractus solitarius in autonomic function; and the gigantocellular tegmental field (FTG) of the pontine reticular formation, which is associated with rapid eye movement sleep. The synaptic development will be characterized 1) in the normal developing postnatal rat within the first two months following partuition, and 2) in the postnatal rat after repeated exposures to low levels of oxygen (hypoxia) during the prenatal period. A stereological technique will be used to analyze large areas of the brain stem tissues by a non-biased statistical method which allows the interpretation of the data within a three-dimensional plane. This analysis will be supplemented by subjective analysis of the types of synapses on both dendritic and somatic receptive fields. The purpose of the project is to determine the most critical period of synaptic development in these three brain stem regions and the effect of hypoxia during the most rapid increase in synaptic number and volume. The project studies the interaction of three major factors associated with Sudden Infant Death Syndrome (SIDS).